Rust's killer features is not "the borrow checker". That idea was just stolen from Cyclone. Rust is basically a semi ml kind of language in the c++ space. I dont see many "killer features" in rust outside the saner type system.

Its basically a better language for software you write in C at the cost of horrible compile times.

The killer feature is definitely memory safety in a systems programming language. That was pretty much thought impossible before Rust came along, and even today there is essentially no competition offering both memory safety and C performance, which requires no GC really.